JP2687744B2 - Mobile satellite communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile satellite communication system having an improved data transfer method.

[0002]

2. Description of the Related Art A mobile satellite communication system comprises a large number of mobile stations, a central station and a network control station. The central station communicates with individual mobile stations via communication satellites. The network control station has a role of controlling and controlling all of these communications.

By the way, the central station transmits various information to the mobile station in the broadcast mode. This signal is called an outbound signal. Although the type of information varies depending on the system, in general, time information such as universal time is often incorporated in this outbound signal and used for various purposes such as time display at a mobile station.

FIG. 2 shows an example of a state in which time information is incorporated in an outbound signal. Generally, the control field C is placed at the beginning of one frame F on the time axis.
Is provided and various information other than the data D is inserted therein. The time information T may be inserted in this control field C.

When the central station is functionally divided, it is divided into a transmitter / receiver part for satellite communication, a modulator / demodulator part for satellite communication, and a part for controlling them. Here, attention is paid to the modulation / demodulation unit and the control unit.

The modulator for the outbound signal in the modulator / demodulator modulates and outputs the outbound signal containing the time information sent from the controller. At this time, the timing shift from the input to the output of the signal can be reduced to a negligible level, or becomes a fixed value even if it is slightly large.

The control section requires a frame timing signal to create time information. Therefore, the control unit is provided with a frame timing generator. The control unit creates an outbound signal including time information with the frame timing signal as a time reference, and sends the outbound signal to the modulation / demodulation unit. Considering the delay time in the above-mentioned modulator and the time of about 240 milliseconds as the propagation time to the communication satellite, if the frame timing signal is offset in the early direction by that amount, the outbound signal will be transmitted by the mobile unit. The timing received by the station can be adjusted to the standard time such as universal time.

In such a conventional mobile satellite communication system, the central station can provide the time information of practically sufficient accuracy to each of the participating mobile stations. Does not occur.

In view of the system configuration, a mobile satellite communication system is conventionally proposed in which a control unit is installed in a network control station, a modulation / demodulation unit and a transmission / reception unit form a central station, and both stations are connected by an asynchronous line. It had been. In such a mobile satellite communication system, since the control systems are all integrated in the network control station, the configuration of the control system equipment can be rationalized, and the economical efficiency and reliability of the system can be improved. For this reason, the introduction of such mobile satellite communication systems is on the increase in the future.

[0010]

However, in such a mobile satellite communication system, an outbound signal or a clock signal input to the modulator has a jitter, and an error such as data loss or repetition occurs at the output of the modulator. May occur. Therefore, a failure such as loss of frame synchronization occurs in all mobile stations, and a momentary disconnection of the line is likely to occur, which is a serious problem in the system configuration.

Therefore, an object of the present invention is to provide a mobile satellite communication system capable of transmitting a correct outbound signal without data loss or repetition.

[0012]

According to the present invention, a control unit for generating data for satellite communication and a central unit for communicating with a plurality of mobile stations via a communication satellite are connected to the control unit by an asynchronous line. In a satellite communication system composed of a station, a central station, a modulator that modulates an outbound signal containing the time information sent from the control unit in a part of the frame, and a frame sent from the control unit as well. A PLL circuit that generates a clock signal based on a timing signal indicating a timing, a frame timing generation circuit that counts the clock signal by one frame and reproduces a frame timing signal, and a control circuit that is arranged in front of the modulator and is transmitted from the control unit. The received outbound signal is buffered, and when the time information is found in the content of the signal, it is stored in the frame timing generation circuit. It is composed of a data receiving circuit for sending a reset signal for resetting the.

That is, in the present invention, a PLL circuit is prepared in the central station to generate a clock signal based on a signal indicating a frame timing sent from the control section, and an outbound signal is of an asynchronous connection type. . Then, the central station reproduces a clean clock that does not cause jitter, and modulates the outbound signal 18 input from the control unit using this clock so that a correct outbound signal without data loss or repetition can be transmitted. .

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the configuration of a mobile satellite communication system according to an embodiment of the present invention. The mobile satellite communication system 11 has a configuration in which a network control station 12 and a central station 13 are connected by an asynchronous line 14. The network control station 12 is provided with a frame timing generation circuit 15 as is conventional. The frame timing signal 16 output from the frame timing generation circuit 15 is input to the data transmission circuit 17, and the outbound signal 18 is created based on this.

The central station 13 has a data receiving circuit 21 for receiving data, a PLL circuit 22 for generating a clock based on the frame timing, a modulator 23 for modulating the received data, and a frame for setting the frame timing. A timing generation circuit 24 is provided.

In the mobile satellite communication system having such a configuration, at the beginning of each frame of the outbound signal 18 transmitted from the network control station 12, as in the conventional frame configuration shown in FIG. The time information of is created and inserted based on the frame timing.
The frame timing signal may be a delay generated in the modulator 23 or the data receiving circuit 21 in the central station or the central station 13
Considering the round trip delay from the mobile station to the mobile station, the offset is made earlier by that amount.

The outbound signal 18 is not sent to the central station 13 as it is, but is sent using an asynchronous data transfer method such as start-stop synchronization. The data transmission circuit 17 in the network control station 12 does this.

The asynchronous data output from the data transmission circuit 17 is input to the data input circuit 21 of the central station via the asynchronous line 14. In the data input circuit, while watching the contents of the input asynchronous outbound signal 18, this is temporarily buffered. Then, when the time information at the beginning of the frame is found in the content of the received outbound signal 18, a reset signal is sent to the frame timing generation circuit 24.

The frame timing generation circuit 24 uses a PL
One frame length is counted by the clock signal sent from the L circuit 22 and a frame timing signal is generated. This frame timing signal is input to the data input circuit 21. The reset signal is received by the frame timing generation circuit 24 only once, and the second and subsequent ones are not received. Otherwise, the timing of the frame timing signal will be swung by the reset signal including the jitter from the signal passing through the asynchronous line 14. When this happens,
This will cause errors such as omissions and repetitions in the transmitted outbound signal.

The data receiving circuit 21 reads the buffered data in order from the data at the beginning of the frame by the frame timing signal output from the frame timing generating circuit 24 and sends it to the modulator 23. The clock signal reproduced by the PLL circuit 22 is used for reading at this time.

On the other hand, the reproduction of the clock signal is performed as follows. That is, the P station located in the central station 13
A clock component is sent from the network control station 12 to the LL circuit 22 via the asynchronous line 14. Specifically, for example, data in the form of "1, 0, 1, 0, ..." Has a frequency component of one half of the clock signal. Therefore, if such a signal is input to the central station 13, even if it is an asynchronous signal and contains jitter,
The PLL circuit 22 can sufficiently reproduce the original clock signal.

When the clean clock signal is reproduced in this way, it can be used as the read clock of the data receiving circuit 21, the clock signal of the modulator 23, and the clock signal of the frame timing generating circuit 24. You can

[0024]

As described above, according to the present invention, a correct outbound signal without jitter can be transmitted even if the modulation / demodulation unit for satellite communication and the control unit for generating an outbound signal are connected by an asynchronous line. it can. Therefore, it is possible to configure a mobile satellite communication system that does not give an obstacle such as a momentary interruption to the mobile station.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of a mobile satellite communication system according to an embodiment of the present invention.

FIG. 2 is a frame configuration diagram of an outbound signal in which time information is incorporated at the tip of the frame.

[Explanation of symbols]

 11 Mobile Satellite Communication System 12 Network Control Station 13 Central Station 14 Asynchronous Line 24 Frame Timing Generator

Claims (1)

(57) [Claims] 1. A central station comprising a control section for generating data for satellite communication, and a central station connected to the control section by an asynchronous line and communicating with a plurality of mobile stations via communication satellites. Generates a clock signal based on a modulator that modulates the outbound signal that contains the time information sent from the control unit as part of the frame, and a timing signal that also indicates the frame timing sent from the control unit. A PLL circuit, a frame timing generation circuit that counts the clock signal for one frame and reproduces a frame timing signal, and an outbound signal sent from the control unit that is arranged in front of the modulator and buffers the outbound signal. When the time information is found in the contents of the data, a data signal is sent to the frame timing generation circuit for resetting it. A mobile satellite communication system, comprising: